Hawaii Wastewater Treatment Operator
Certification (Hawaii DOH) Newest 2025 –
2026 Updated Questions From Actual Exams
Complete 100 Questions And Correct Detailed
Answers (Verified Answers) |Already Graded
A+||Brand New!!
1. What is the primary purpose of wastewater treatment in Hawaii?
A. Increase water salinity
B. Remove contaminants to protect public health and environment
C. Produce drinking water directly
D. Eliminate all microorganisms completely
**✔ B. Remove contaminants to protect public health and environment
[Correct answer: B – Wastewater treatment focuses on reducing physical,
chemical, and biological contaminants to safe levels before discharge or reuse.]
2. Which process is considered preliminary treatment?
A. Chlorination
B. Screening
C. Aeration
D. Sedimentation
**✔ B. Screening
[Correct answer: B – Screening removes large solids like rags and plastics before
primary treatment.]
, 3. The main purpose of primary sedimentation is to:
A. Kill pathogens
B. Remove dissolved solids
C. Settle suspended solids by gravity
D. Add oxygen to wastewater
**✔ C. Settle suspended solids by gravity
[Correct answer: C – Primary clarifiers allow solids to settle and scum to rise for
removal.]
4. Activated sludge treatment primarily uses:
A. Chemical oxidation
B. Microorganisms
C. UV radiation
D. Filtration membranes only
**✔ B. Microorganisms
[Correct answer: B – Activated sludge relies on aerobic bacteria to break down
organic matter.]
5. What is the function of aeration tanks?
A. Remove grit
B. Provide oxygen for microbial activity
C. Store sludge permanently
D. Disinfect wastewater
**✔ B. Provide oxygen for microbial activity
[Correct answer: B – Aeration tanks supply oxygen to support aerobic digestion of
organics.]
, 6. BOD stands for:
A. Biological Oxygen Demand
B. Biochemical Oxygen Demand
C. Basic Organic Digestion
D. Biochemical Oxidation Density
**✔ B. Biochemical Oxygen Demand
[Correct answer: B – BOD measures oxygen required by microorganisms to break
down organic matter.]
7. High BOD in wastewater indicates:
A. Low organic pollution
B. High organic pollution
C. High chlorine levels
D. Low microbial activity only
**✔ B. High organic pollution
[Correct answer: B – Elevated BOD indicates large amounts of biodegradable
organic material.]
8. The purpose of a clarifier is to:
A. Mix chemicals
B. Increase oxygen levels
C. Separate solids from liquid
D. Destroy bacteria
**✔ C. Separate solids from liquid
[Correct answer: C – Clarifiers allow solids to settle and clarified water to
overflow.]
, 9. Sludge digestion primarily reduces:
A. Color
B. Pathogens and organic content
C. pH only
D. Flow rate
**✔ B. Pathogens and organic content
[Correct answer: B – Digestion stabilizes sludge by reducing volatile solids and
pathogens.]
10.In wastewater treatment, grit removal targets:
A. Oils
B. Sand and gravel
C. Dissolved salts
D. Bacteria
**✔ B. Sand and gravel
[Correct answer: B – Grit chambers remove heavy inorganic particles like sand.]
11.A sudden drop in dissolved oxygen (DO) may indicate:
A. Improved treatment efficiency
B. Increased organic loading
C. Reduced influent flow
D. High chlorine residual
**✔ B. Increased organic loading
[Correct answer: B – More organic waste consumes oxygen, lowering DO levels.]
12.What is the ideal purpose of secondary treatment?
A. Remove floating debris
B. Remove dissolved and colloidal organics
Certification (Hawaii DOH) Newest 2025 –
2026 Updated Questions From Actual Exams
Complete 100 Questions And Correct Detailed
Answers (Verified Answers) |Already Graded
A+||Brand New!!
1. What is the primary purpose of wastewater treatment in Hawaii?
A. Increase water salinity
B. Remove contaminants to protect public health and environment
C. Produce drinking water directly
D. Eliminate all microorganisms completely
**✔ B. Remove contaminants to protect public health and environment
[Correct answer: B – Wastewater treatment focuses on reducing physical,
chemical, and biological contaminants to safe levels before discharge or reuse.]
2. Which process is considered preliminary treatment?
A. Chlorination
B. Screening
C. Aeration
D. Sedimentation
**✔ B. Screening
[Correct answer: B – Screening removes large solids like rags and plastics before
primary treatment.]
, 3. The main purpose of primary sedimentation is to:
A. Kill pathogens
B. Remove dissolved solids
C. Settle suspended solids by gravity
D. Add oxygen to wastewater
**✔ C. Settle suspended solids by gravity
[Correct answer: C – Primary clarifiers allow solids to settle and scum to rise for
removal.]
4. Activated sludge treatment primarily uses:
A. Chemical oxidation
B. Microorganisms
C. UV radiation
D. Filtration membranes only
**✔ B. Microorganisms
[Correct answer: B – Activated sludge relies on aerobic bacteria to break down
organic matter.]
5. What is the function of aeration tanks?
A. Remove grit
B. Provide oxygen for microbial activity
C. Store sludge permanently
D. Disinfect wastewater
**✔ B. Provide oxygen for microbial activity
[Correct answer: B – Aeration tanks supply oxygen to support aerobic digestion of
organics.]
, 6. BOD stands for:
A. Biological Oxygen Demand
B. Biochemical Oxygen Demand
C. Basic Organic Digestion
D. Biochemical Oxidation Density
**✔ B. Biochemical Oxygen Demand
[Correct answer: B – BOD measures oxygen required by microorganisms to break
down organic matter.]
7. High BOD in wastewater indicates:
A. Low organic pollution
B. High organic pollution
C. High chlorine levels
D. Low microbial activity only
**✔ B. High organic pollution
[Correct answer: B – Elevated BOD indicates large amounts of biodegradable
organic material.]
8. The purpose of a clarifier is to:
A. Mix chemicals
B. Increase oxygen levels
C. Separate solids from liquid
D. Destroy bacteria
**✔ C. Separate solids from liquid
[Correct answer: C – Clarifiers allow solids to settle and clarified water to
overflow.]
, 9. Sludge digestion primarily reduces:
A. Color
B. Pathogens and organic content
C. pH only
D. Flow rate
**✔ B. Pathogens and organic content
[Correct answer: B – Digestion stabilizes sludge by reducing volatile solids and
pathogens.]
10.In wastewater treatment, grit removal targets:
A. Oils
B. Sand and gravel
C. Dissolved salts
D. Bacteria
**✔ B. Sand and gravel
[Correct answer: B – Grit chambers remove heavy inorganic particles like sand.]
11.A sudden drop in dissolved oxygen (DO) may indicate:
A. Improved treatment efficiency
B. Increased organic loading
C. Reduced influent flow
D. High chlorine residual
**✔ B. Increased organic loading
[Correct answer: B – More organic waste consumes oxygen, lowering DO levels.]
12.What is the ideal purpose of secondary treatment?
A. Remove floating debris
B. Remove dissolved and colloidal organics
